Electric heater assembly



July 1, 1969 M. N. HUMMEL 3,453,417

ELECTRIC HEATER ASSEMBLY Fned Dec. v, 1966 July 1, 1969 M. N. HUMMEL3,453,417 l ELECTRIC HEATER ASSEMBLY Filed Dec. v, 196e sheet 3 of 2United States Patent O i 3,453,417 ELECTRIC HEATER ASSEMBLY Matt N.Hummel, Glenview, Ill., assignor to Acra Electric Corporation, FranklinPark, Ill., a corporation of Illinois Filed Dec. 7, 1966, Ser. No.599,801 Int. Cl. Hb 3/06 U.S. Cl. 219-536 7 Claims ABSTRACT OF THEDISCLOSURE Electric heater elements or assemblies of the strip or bandtype are commonly used in food warmers, vending machines, refrigerationcompressors, and other locations Where a concentrated application ofheat is desired. The strip or band type heater element is particularlysatisfactory because it has a relatively thin flat structure whichprovides a maximum contact area for heat transfer between the heaterelement and the object to be heated. This relatively large at heattransfer area promotes rapid thermostatic response of the heater whileminimizing heat loss through radiation.

Prior art band or strip-type heater elements commonly include a resistorwire which is mounted on or sandwiched between a pair of mica heaterplates. The plates and resistor wire are usually encased within ametallic sheath. The sheath generally includes an upper terminal plateand a lower base plate. The separate upper and lower sheath plates areinterconnected by longitudinally extending flanges which are integrallyformed with the base plate and are folded into overlapping engagementwith opposite longitudinally extending sides of the upper terminalplate. Two longitudinally extending joints are formed between theilanges of the base plate and the terminal plate. These joints areusually sealed to prevent moisture from leaking into contact with theplates and resistor wire.

These prior art heater elements, while being particularly advantageousfor many applications, are relatively expensive and dicult tomanufacture. The manufacturing expense and diculty is due, in part atleast, to the construction of the metallic sheath -and plates used inthe heater element. The manufacturing of the heater element requiresthat the mica plates and the upper terminal plate be centrallypositioned on the base plate of the sheath. Then the longitudinallyextending outer edges of the base plate are bent or folded intooverlapping relationship with the terminal plate. After these steps havebeen performed, the joint between the overlapping base plate andterminal plate are sealed to provide a waterproof heater element. Therelatively large number of manufacturing operations and joints in thesheath all increase the cost of the heater element.

Therefore, it is an object of this invention to provide a relativelyinexpensive band or strip-type heater element.

Another object of this invention is to provide a sheath for a band orstrip-type heater which has a relatively large heat transfer area andwhich is inexpensive to fabricate.

3,453,417. Patented July l, 1969 Another object of this invention is toprovide a waterproof heater element which can be easily andinexpensively fabricated.

These and other objects and features of the invention will become moreapparent upon a consideration of the =following detailed descriptiontaken in connection with the accompanying drawings wherein:

FIG. l is a perspective view of a food Warmer in which a plurality ofcontainers of food are warmed by la heater assembly forming a preferredembodiment of the invention;

FIG. 2 is an enlarged perspective view of the heater structure orassembly used in the food warmer of FIG. l;

FIG. 3 is an enlarged cross-sectional view of a sheath used with theheater assembly of FIG. 2, the sheath being shown in an open positionbefore a heating element has been inserted into the sheath;

FIG. 4 is an enlarged cross-sectional view of the sheath in the openposition, similar to FIG. 3, with the heating element inserted orpositioned in the sheath;

FIG. 5 is an enlarged cross-sectional view, along the line `5 5 of FIG.2, illustrating the interrelationship of the heating element and thesheath when the sheath is in a closed position;

FIG. 6i is an enlarged perspective view illustrating the relationship ofthe sheath to a longitudinally outwardly extending mounting or connectorend section of the heater assembly;

FIG. 7 is an enlarged perspective view, similar to FIG. 2, of a heaterassembly which forms a second embodiment of the invention;

FIG. 8 is an enlarged elevational view illustrating the relationship ofa toggle-type mounting clamp assembly to the heater assembly of FIG. 2;

FIG. 9 is an enlarged plan view of the clamp assembly of FIG. 8; and

FIG. 10 is an enlarged cross-sectional vie-w, taken along the line 10-10of FIG. 8, illustrating an interconnection between two sections of theclamp assembly.

Referring now to the drawings in greater detail, a food warmer 20 isvshown in FIG. 1. The food warmer 20 includes a tank 22 into which aplurality of receptacles or containers 24 project for holding food. Aheater assembly or structure 30, forming a preferred embodiment of theinvention, is mounted on a lower end portion of each of the containers24 to heat the contents of the containers. The tank 22 is filled withwater or another suitable iluid to promote conduction of heat aroundupwardly extending sides of the containers 24.

The heater assembly is shown in greater detail in FIG. 2. The heaterassembly 30 includes a ilexible metal sheath or cover structure 32 whichcan be formed of aluminum, steel, or any of the many suitablecommercially available metal alloys. A pair of molded sealing blocks orbodies 34 and 36 are mounted at oppoiste ends of the sheath 32 to sealthe ends of the sheath. The blocks 34 and 36 are formed of a suitableelestomeric compound, such as any one of the commercially availablesilicone or neoprene ysynthetic rubber compounds. A pair of mounting orconnector end sections 38 and 40 extend longitudinally outwardly fromthe blocks 34 and 36 to facilitate mounting the heater assembly 30 on abody, similar to the containers 24, which is to be heated. A pair ofconnector or lead wires 42 and 44 also extend longitudinally outwardlyfrom the blocks 34 and 36. The lead wires 42 and 44 are connected to aheating element 50 which is best seen in FIG. 5. The heating element 50can advantageously be formed of a helical coil 52 of nickel chromiumresistance Wire which is surrounded with an electrically insulatingsleeve 54 of fiberglass. The heating element 50 extends forsubstantially the entire length of a central heating section 60 (seeFIG. 2) of the heater assembly 30.

3 As will be apparent to those skilled in the art, the coil 52 is heatedby a ow of electrical current through the coil when the lead lwires 42and 44 are connected to a source of electrical energy. Heat from thecoil 52 is then conducted through the sheath 32 to the body which is tobe heated.

The sheath 32 is illustrated, in FIG. 3, in an opened position beforethe heating element 50 has been inserted into the sheath. The sheath 32is a unitary structure which includes a base section 66 integrallyformed with a body section 68. The ybase section 66 and body section 68are interconnected by a longitudinally extending fold or pivotal hingesection 70 which enable-s the body section 68 to be pivoted relative tothe base section 66 from the open position shown in FIG. 3 to a closedposition shown in FIG. 5. The fold or hinge section 70 also provides aWater-tight connection between the base section 66 and the body section68. The base section 66 includes a oor or mounting wall section 74 whichis connected to a leg ange or flap section 76 by a corner or hingesection 80. The body section 68 includes a central U-shaped heatingelement receiving section or protuberance 84. A pair of longitudinallyextending flange arms `or sides 86 and 88 are connected to generallyparallel leg sections 90 and 92 of the U-shaped heating elementreceiving protuberance 84. The leg sections 90 and 92 of theprotuberance 84 extend perpendicularly to the flange arms 86 and 88 andare connected to the flange arms 86 and 88 by corner sections 96 and 98which dene an inner open end or mouth 100 of the protuberance 84. Anouter end of the protuberance is enclosed by a semicircular end orconnector wall 102 to complete the generally U-shaped heating elementreceiving protuberance 84.

The heating element 50 is inserted or mounted in the longitudinallyextending protuberance 84 -when the sheath -or `cover structure 32 is inthe open position, see FIG. 4. The heating element 50 is inserted intothe protuberance 84 by moving the heating element through an arcuateopening 108 which extends between the flange or ap 76 and the flange armor slide 88. After the heating elelment 50 has been moved to a positionintermediate the body `section 68 and base section 66, the heatingelement 50 is laid into the longitudinally extending protuberance 84.The longitudinally extending protuberance 84 is shaped to receive theheating element 50 so that the leg sections 90 and 92 of theprotuberance extend tangentially from the heating element -while thesemicircular end wall 102 of the protuberance engages the outer surfaceof the heating element.

Once the heating element 50 has been positioned in the protuberance 84,the body section 68 is pivoted about the hinge or fold 70 to close theopening 108 and position the ange arms 86 and 88 into confrontingjuxtaposition with the oor 74 of the base section 66, as shown in FIG.5. After the body `section 68 has been pivoted or rotated to the closedposition shown in FIG. 5, the heating element 50 is enclosed by theprotuberance 84 and the oor 74 of the base section 66 which blocks thepreviously open end or mouth 100 of the protuberance 84. It should benoted that the insulation 54 of the heating element 50 extends throughthe mouth 100 into abutting engagement with an inner surface of theiioor or mounting wall 74. The ange armor flap 76 is then pivoted aboutthe longitudinally extending hinge section 80 to move an inner Isurface114 of the flange 76 into confronting juxtaposition with an outersurface 116 of the flange arm 88. The resulting joint between the ap 76and ange arm 88 is sealed by a water and heat resistant adhesive layer118 to securely interconnect the base section 66 and body section 68 ofthe sheath or covering structure 32.

When the heating element 50 is energized heat is radiated from theresistor coil 52 outwardly to the base section 66 and body section 68 ofthe heater assembly 30. This heat from the coil 52 is conducted by therelatively wide longitudinally extending area of the mount- 4 ing wall74 of the base section 66 to a body which is to be heated. Byexperimentation it has been determined that the heater assembly 30should be positioned with the mounting Wall 74 in close abuttingjuxtaposition with the body to be heated. Air gaps between the mountingwall 74 and the body to be heated cause poor heat transfer, lower theefficiency of the heater assembly and may shorten the operating life ofthe heater assembly. To prevent the occurrence of these air gaps, anouter surface 122 of the mounting wall 74 is coated with a layer 124 ofa heat and water resistant adhesive which securely connects the mountingWall 74 to the body to be heated.

After the heating element 50 has been mounted in the sheath 32 in themanner previously explained, the blocks 34 and 36 are molded onto theouter end of the sheath 32 to seal or close the sheath. Thelongitudinally extending joint between the flap 76 and the flange arm 88is sealed by a longitudinally extending layer of water resistantadhesive 118 so that the water cannot seep into the interior of thesheath 32 through the joint between the base and body section. Since thelongitudinally outer ends of the sheath are sealed by the blocks 34 and36 which are molded in tight sealing engagement with the leads 42 and44, the sheath 32 is completely Waterproof. It should be noted that thehinge 70 is integrally formed with the base section 66 and body section68 so that water cannot seep into the interior of the sheath 32 alongthe side of the sheath which is opposite from the layer of adhesive 118.

The longitudinally outwardly extending mounting or end sections 38 and40 of the heater assembly 30 are integrally formed with the sheath 32,as is best seen in FIG. 6. The end sections 38 and 40 are in fact acontinuation of the mounting wall 74 of the base section 66. As will beexplained in greater detail subsequently the end sections 38 and 40 areadapted for engagement with a clamping unit to mount the heater assembly30 on cylindrical bodies, such as the containers 24 of FIG. 1.

A heater assembly forming a second embodiment of the invention is shownin FIG. 7. The heater assembly 150 is generally similar in constructionto the heater assembly 30. However, the end portions and joints of theheater assembly 150 are not sealed. Therefore, the heater assembly 150is not waterproof as is the heater assembly 30. The heater assemblyincludes a base section 152 having a mounting wall 154 and a bodysection 156 having a heating element receiving protuberance 160. Thebase section 152 and the body section 156 are interconnected by a ap orflange 164 to provide an integral sheath or covering structure 170. Aheating element, similar to the heating element 50 of the embodiment ofFIGS. 2 through 6, is mounted within the protuberance 160. A pair oflead wires 172 and 173 connect the heating element to a source ofelectrical energy.

The heater assembly 150 is provided with a plurality of apertures 174and 176 which extend through opposite sides of the heater assembly tofacilitate the mounting of the heater assembly on a body which is to beheated. The apertures or holes 174 extend through the ap 164, a sideportion of the body section 156 and the mounting wall or floor 154 ofthe base section 152. The holes or apertures 176 on the opposite side ofthe heater assembly 150 extend through only a side flange of the bodysection 156 and the mounting wall 154 of the base section 152. Althoughthe heater structure 150 is intended for use in locations wherein theheater is not `submerged in water or other fluid, it will be apparent tothose skilled in the art that the heater assembly 30 of FIG. 2 could bereadily provided With apertures, similar to the apertures 174 and 176,to mount the heater assembly 30 on a body to be heated. Of course, sincethe heater assembly 30 is intended for use in locations where it iscontacted by uid, a heat and fluid resistant layer of adhesive would beprovided between the base and body sections of the heater assemblieswhere the apertures, similar to the apertures 174 and 176, extendthrough the base and body sections to seal olf the apertures from theinterior of the sheath 30.

A toggle type clamp assembly 180 for the heater assemblies 30 and 150 isshown in FIGS. 8 through 10 in connection with the first embodiment ofthe heater assembly. The clamp assembly 180 includes a clamp or actuatorarm 184 which is mounted for pivotal movement about a pin 186 whichextends through a central axis of a pair of spaced apart outwardlyextending flanges or ears 190 which are integrally formed with andextend from the actuator arm 184 (see FIGS. 8 Iand 10). A resilientgenerally U-shaped frame or connector section 194 engages the ears 190of the actuator arm 184. The frame 194 has a pair of inwardly extendingconnector fingers 196 which project toward each other to engage a pairof apertures or holes 198 in the ears 190 of the actuator arm 184. Theframe 194 is connected to the end section 38 of the heater assembly 30and the pin 186 is connected to the opposite end section 40 of theheater assembly 30. Thus, the two ends of the heater assembly 30 areinterconnected by the clamp assembly 180 to form an annular heaterstructure which can be readily mounted on cylindrical bodies, such asthe receptacles 24 of FIG. 1.

When the actuator arm 184 is moved to the open position, illustrated indashed lines in FIG. 8, the aperture 198 is spaced apart from the endsection 40. This loosens the heater assembly 30 on the cylindrical bodyby increasing the circumference of the heater assembly. When theactuator arm 184 is rotated to the closed position shown `in solid linesin FIG. 8, the aperture 198 is moved to a position adjacent to the endsection 40 of the heater assembly 30 to decrease the circumferentialdimension of the heater assembly and, consequently, tighten the heaterassembly on the body on which it is mounted. When the clamp assembly 180is in the closed position the aperture 198 is offset radially inwardlyrelative to the end section 40. Therefore an increased circumferentiallydirected force, due to thermal expansion or other causes, on the heaterassembly 30 merely pulls the actuator arm in the direction of the arrowin FIG. 8 to tighten the clamp assembly in a toggle action which is wellknown per se to those skilled yin the art. A pair of resilient springs200 and 202 are integrally formed with the frame structure 194. Thesprings 200 and 202 allow the heater assembly 30 and the body on whichit is mounted to thermally expand and contract at different rateswithout damage to the heater assembly. The springs 200 and 202 enablethe heater assembly 30 to resiliently expand and contractcircumferentially with expansion and contraction of the body in whichthey are mounted due to thermal effects. However, the springs 200 and202 are sufficiently stiff, that is, have a high enough spring rate, tomaintain the heater assembly 30 in close abutting engagement with thebody to be heated. It should be noted that the toggle type clampassembly 180 pulls the heater assembly into tight abutting engagementwith the body on which it is mounted when the actuator arm 184 is movedfrom the open position indicated in dashed lines in FIG. 8 to the closedposition indicated in solid lines in FllG. 8.

For purposes of affording a more complete understanding of theinvention, it is advantageous now to provide a functional description ofthe mode in which the component parts of the invention cooperate. Whenthe heater assembly 30 is manufactured or fabricated the sheath willinitially be in the open position shown in FIG. 3. With the sheath 32 inthis position the heating element 50 can be readily located in theprotuberance 84. The body section 68 of the sheath 32 will then bepivoted toward the base section 66 of the sheath 32 about the hingesection 70 to position the flange arms 86 and 88 in abutting engagementwith the mounting wall 74 of the base section 66. A layer of adhesive118 will then be applied to an outer surface 116 of the flange arm 88.Next the flap 76 will be pivoted about the hinge 80 so that an innersurface 114 of the flap is located in juxtaposition with the outersurface 116 of the ange arm 88. When the flap 76 is in this position,the joint between the flap 76 and the flange arm 88 will be sealed bythe layer of adhesive 118. The end portions of the sheath 32 will besealed by molding the blocks 34 and 36 around the ends of the sheath andleads 42 and 44 which are connected to the heating element 50. The clampassembly 180 is then connected to the flexible end sections 38 and 40 ofthe heater assembly and layer of adhesive 124 is advantageously appliedto the outer surface 122 of the base section 66 to facilitate securingthe mounting wall 74 to a body which is to be heated.

When the heater assembly is to be mounted on a body which is to beheated, the flexible sheath 32 of t-he heater assembly will be bent toconform to the configuration of the body. The frame 194 of the clampassembly 180 will then be connected to the actuator arm 184 of the clampassembly with the actuator arm in the open position indicated by thedashed lines in FIG. 8. Next, the actuator arm 184 will be pivoted orrotated' to the closed position, indicated by solid lines in FIG. 8, todraw the heater assembly 30 into secure abutting engagement with thebody which is to be heated.

The second embodiment of the heater assembly is assembled in the samemanner as was previously set forth for the embodiment 30 of the heaterassembly. However, it is contemplated that the heater assembly 150 willbe used in locations which do not require a waterproof heater assemblyso that the manufacturing steps of molding the blocks 34 and 36 on theend portion of the heater assembly are omitted as is the layer ofadhesive between the flap and the body section. The heater assembly 150is provided with a plurality of apertures 174 and 176 which extendthrough the base section 152 and body section 156 of the heaterassembly. The apertures 174 and 176 are particularly advantageous forsuspending the heater element 150 to heat the air within an enclosure.It should be noted that when the apertures 174 and 176 are utilized witha suitable connection means for fastening the heater assembly 150 to abody having a different coefficient of thermal expansion than the heaterassembly 150, only one end of the heater assembly should be tightlyfastened to the body which is to be heated. The other end of the heaterassembly must be loosely fastened to the body which is to be heated t0enable the heater assembly to expand freely during a heating cycle.

The heater assemblies 30 and 150 are normally connected to power sourceswhich provide a heater output of approximately one to twenty-live wattsper square inch of surface of the mounting wall 74 of the heater. Ofcourse, the output of the heater takes into account the type of materialwhich is to be heated, the surface characteristics of the surfacecontainer or mass in which the materials are held, and the environmentaland operating conditions in which the heater assembly is operated. Theoutput of the heater will, to some extent, determine the metal fromwhich the sheaths 32 and 170 of the heater assembly are formed. Analuminum sheath should not be operated at temperatures in excess ofapproximately 550 degrees Fahrenheit while a stainless steel sheath canbe utilized at operating temperatures of about 1,200 degrees Fahrenheit.Of course, the material from which the adhesive layer 118 and the blocks34 and 36 are formed will also be determined by the temperature at whichthe heater assembly 30 is to be operated.

It is contemplated that heating elements having a structure other thanthe specific structure set forth for the heaing element 50 will be usedwith the heater assembly 30. It is also contemplated that clampingassemblies, other than the toggle type clamping assembly 180 will beused with the heater assembly 30. Of course, the composition ofthevarious components of the heater assembly can be varied from thespecific examples given herein. Therefore, while particular embodimentsof the invention have been shown, it should be understood that theinven- 7 tion is not limited thereto since many modications may be made;and it is contemplated to cover by the appended claims any suchmodiiications as fall within the true spirit and scope of the invention.

What is claimed is:

1.A heater assembly comprising: a longitudinally extending electricalresistance member providing a heating element; a longitudinallyextending metallic sheath enclosing said heating element, electricallynonconductive insulative means between said heating element and sheath,said metallic sheath including a at longitudinally extending basesection and a longitudinally extending body section integrally formedwith said base section, said body section including a generally U-shapedcentral section for receiving said heating element and a pair ofoutwardly extending coplanar arm sections connected to opposite legs ofthe U-shaped body section and positioned in juxtaposition with said basesection, one of said arm sections being h ingedly connected to said basesection, and a second of said arm sections being positioned in sealingengagement with an inner surface of a ange section which is integrallyformed with and hingedly connected to said base section; alongitudinally extending layer of a heat resistant waterproof adhesivemeans sealingly interconnecting an outer surface of said second armsection and an inner surface of said flange section; iirst and secondlead wires for connecting opposite ends of said heating element to asource of electrical power; a first body of elastomeric materialenclosing a first end portion of said sheath and a portion of said firstlead wire to seal a first end of the heater assembly; a second body ofan elastomeric material enclosing a second end portion of said sheathand a portion of said second lead wire to seal a second end of theheater assembly; a first mounting element extending outwardly from saidfirst body of elastomeric material to facilitate mounting the heaterassembly on a body to be heated; and a second mounting element extendingoutwardly from said second body of elastomeric material to furtherfacilitate mounting the heater assembly on a body to be heated.

2. A heater assembly as set forth in claim 1 further including: a toggletype clamp assembly releasably interconnecting said first and secondmounting elements, said toggle type clamp including an actuator armmounted for pivotal `movement about an outermost end portion of saidfirst mounting element, and a body means connected to said secondmounting element engaging an aperture means in said actuator arm, saidaperture means beinyg oiset relative to an axis of rotation of saidactuator arm, said actuator arm being pivotal from a released positionin which said aperture means and said body means of said toggle clampare spaced apart from said rst mounting element to a closed position inwhich said aperture means and said body means of said clamp assembly arepositioned adjacent to said irst mounting element to securely clamp theheater assembly to a body to be heated.

3. A heater assembly as set forth in claim 1 further including:resilient clamp means interconnecting said first and second mountingelements for securing the heater assembly to a body to be heated.

4. A heater assembly as set forth in claim 1 further including: a layerof heat resistant pressure sensitive adhesive mounted on an outersurface of said base sec'- tion to still further facilitate the mountingof a heater assembly on a body to be heated.

5. A heater assembly as set for-th in clairn 1 wherein: said rst andsecond mounting elements are integrally formed with said base section.

6. A heater assembly as set forth in claim 1 further including: aplurality of longitudinally spaced apertures extending through saidiirst and second sections to facilitate mounting the heater assembly.

7. A heater assembly as set forth in claim 1 further including: a pairof ex-ible mounting sections integrally formed with said second sectionand extending longitudinally and outwardly of said irst section, saidmounting sections being adapted for engagement with a clamp assembly tomount the heater assembly on a body to be heated.

References Cited UNITED STATES PATENTS 1,473,866 11/1923 Phelps 338-2511,494,939 5/1924 Abbott 219-540 2,019,913 11/1935 Kmrbafy 219-5402,742,561 4/1956 Hafer 2191-536 X 2,851,577 9/1958 Bolas e1 a1. 219540 X2,876,322 3/1959 Boggs 33s-274 X 2,832,376 4/1959 Charbonneau 219-535 X3,010,007 11/1961 Theodore 61 a1. 219-544 X 3,029,303 4/,1962 Severino174-97 3,214,571 10/1965 indo@ 219-544 3,370,156 2/1968 Graves 219-540FOREIGN PATENTS 402,321 11/1933 Great Britain.

VOLODYMYR Y. MAYEWSKY, Primary Examiner.

U.S. C.l. X.R.

